This invention relates to the deposition of thin layers from reactive gases, and, more particularly, to a system for delivering such gases to a deposition reactor.
In chemical vapor deposition (CVD), one or more reactive gases is contacted to a substrate that has been energized, as by heating. With the proper selection of the reactive gas or gases, the substrate type and temperature, gas partial and total pressures, and other operating parameters, the reactive gases deposit a selected material as a gradually thickening layer onto the surface of the substrate. The deposition continues until the desired thickness is reached.
The reactive gases used in the reactive deposition are provided from either gaseous or liquid sources. Liquid sources have become increasingly popular, as the reactive gases are often safer to handle and less toxic when provided in their liquid forms. Prior to the reactive deposition, the liquid source is heated to produce a vapor of the reactive gas, which is conducted to the substrate and reacted.
Several heretofore unsolved problems have been encountered in delivery systems that utilize liquid sources of the reactive gases. Flow variations in individual gases are sometimes observed, leading to variations in composition of the deposited layer. Deposits can build up in the interior of the delivery system. Contaminants can enter the system during operating transitions such as the changing of sources. Although acceptable deposited structures can often be made in spite of these problems, it would be preferred to improve deposition and delivery system operation through their solution.
There is therefore a need for an improved reactive gas delivery system for use with liquid sources. The present invention fulfills this need, and further provides related inventions.